{ INFORMATICS.MCCME.RU
  Problem statement: http://informatics.mccme.ru/moodle/mod/statements/view3.php?chapterid=2945
  Verdict: Accepted
}
var a:longint;
begin
assign(input,'input.txt');
assign(output,'output.txt');
reset(input);
rewrite(output);
readln(a);
if odd(a) then inc(a) else inc(a,2);
write(a);
end.